1. Field of the Invention
This invention relates to an elongated shaft member which is made from synthetic resin material and comprises a hollow portion, formed inside of the elongated shaft member and substantially coaxial with a center axis, extending in a direction in which the center axis extends, and through-holes formed at ends in the extending direction of the hollow portion and substantially coaxial with the center axis, through which the hollow portion communicates with the outside. More particularly, this invention relates to an elongated shaft member which comprises a main body including a hollow portion, substantially coaxial with a center axis, extending in a direction in which the center axis extends. The main body includes shaft portions formed at ends of the main body respectively, the shaft portions being smaller in diameter than the main body and through-holes formed in the shaft portions respectively, through which the hollow portion communicates with the outside. The through-holes are substantially coaxial with the center axis. The invention relates to a mold, apparatus, and method for molding the elongated shaft member. Even more particularly, this invention relates to a mold, apparatus, and method suitable for molding an elongated shaft member provided with screws on the outer circumferential surface of its main body for conveying a toner, for example.
2. Description of the Prior Art
If an elongated shaft member is produced by cutting and processing a synthetic-resinous cylindrical bar, production costs are raised for synthetic resin material used for producing this elongated shaft member, and the elongated shaft member becomes heavier.
In an elongated shaft member used to convey a toner and the like, it is required to mount a plurality of spiral projections (fins) forming up screws for conveying a toner and the like on the outer circumferential surface of its main body at intervals and, in addition, form shaft portions at ends in the axial direction of the main body. This results in a complicate configuration. Thus, if a synthetic-resinous cylindrical bar is cut and processed to produce an elongated shaft member, many processing steps are taken and accordingly the cost of production is raised because of the complicated configuration of the products.
Heretofore, a method has been known known for molding this type of elongated shaft member integrally as a whole (see Japanese Patent Application Laid-Open Publication No. Hei 5-208460). As shown in FIG. 32, in this method (gas injection method), a gate 2 for supplying molten synthetic resin material is disposed on an extension line of a substantially center axis Oo of a molding cavity 1 of a mold, and a gas supplying pipe (gas supplying nozzle) 3 is connected to the gate 2 from a direction substantially perpendicular to the gate 2.
In this prior art technology, a predetermined amount of molten synthetic resin is measured to be injected into the cavity 1, the molten synthetic resin material 4 is then supplied from the gate 2, and thereafter pressure gas is injected into the molten synthetic resin from the gas supplying pipe 3. As a result, the molten synthetic resin material 4 is pressed onto the whole of an inner wall of the mold by means of the pressure gas and is spread thereon. Accordingly, an elongated shaft member is produced which has a hollow portion therein and has the same outer shape as the shape of the inner surface of the cavity 1.
In other words, as shown in FIG. 33, an elongated shaft member 8 is produced which has a main body 6 including a hollow portion 5 extending in a direction of a center axis O1 and has two small shaft portions 7, formed at both ends of the main body 6 which are smaller in diameter than the main body 6.
However, the elongated shaft member 8 molded according to this prior art technology is liable to suffer curving deformation caused by the non-uniformity of thickness because the pressure gas supplied through the gas supplying pipe 3 flows into the cavity 1 from a direction perpendicular to the center axis O1. Additionally, the elongated shaft member thus molded has a poor appearance because a hole 9 through which the hollow portion 5 communicates with the outside is produced in the outer surface of one of the shaft portions 7 as a result of supplying the pressure gas.
There is a case in which a metallic pipe is inserted into one or both of the ends of the body 6 in order to receive rotational force. When an elongated shaft member 8 is molded in which a metallic pipe 7 is inserted into one end of the body 6, the metallic pipe 7 is set on the side of the cavity 1 far from the gate 2, as shown in FIG. 34, for example. After that, the molten synthetic resin material 4 is injected from the gate 2 shown in FIG. 32, and the pressure gas is injected into the molten synthetic resin 4 staying in the cavity 1 from the gas supplying pipe 3.
However, the molten resin practically measured per molding cycle has fluctuations in quantity. Fluctuations in hollow rate occur in accordance with the fluctuations in quantity. For this mold, molten resin corresponding to 70 percent of the capacity of the cavity 1 is measured and injected so that a resultant molding has a hollow rate of 30 percent in volume. Accordingly, in the case of a large amount of molten resin, a concentration 10 of the molten synthetic resin material 4 occurs in the vicinity of the metallic pipe 7 far from the gate 2. This concentration 10 is difficult to be hardened, and therefore much cycle time for molding is taken. This brings about a rise in production costs. Further, the molding is deformed and becomes inferior in dimensional accuracy because the concentration 10 is considerably shrunk when the resin material thereof is hardened. Further, the finished elongated shaft member has an undesirably thicker part corresponding to the hardened resin of the concentration 10.
On the other hand, in the case of a lesser amount of synthetic resin material to be injected, a less-thickness part occurs in the vicinity of the metallic pipe 7 far from the gate 2.
In a case in which the metallic pipe 7 is inserted into both ends of the elongated shaft member 8, the gate 2 and the gas supplying pipe 3 must be mounted perpendicularly to the center axis Oo. Likewise, in this case, the pressure gas from the gas supplying pipe 3 turns perpendicularly and flows into the cavity 1. Therefore, the molding suffers deformation caused by the non-uniformity of thickness. Additionally, a similar disadvantage occurs because a concentration 10 is generated in the vicinity of the metallic pipe 7 far from the gate 2.